Balchin was near the front for the ten-lap men's race and put in an early surge to test the field after four laps.
With one lap to run the two South Islanders Balchin and Shields shook off the others and set about a titanic contest that was only settled in the final metres with Balchin finally shaking off a tenacious Shields.
Nagel, winner of the national 10km cross country titles four weeks earlier stamped her intentions on the women's race early in the 10k event, clearing out from Lydia O'Donnell and Sally Gibbs. She extended the lead on each lap and won comfortably in 35min 14sec.